Experience with LCLS-II Cavity and Cryomodule Tests at Fermilab

1. Experience with LCLS-II Cavity and Cryomodule Tests at Fermilab E. Harms on behalf of the Fermilab Cryomodule Testing Team TTC meeting at TRIUMF Working Group 1 Session 3 5 February 2019

2. Introduction & Outline Fourteen Fermilab-built cryomodules for LCLS-II have now been tested cold at Fermilab's cryomodule test stand, CMTS1. A summary of test results to date compared against performance criteria, operational experience, and upcoming plans will be shared. • Test bed – CMTS1 • History (plans developed circa 2014) • Summary of Results • Lessons learned • Future Prospects • Summary Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

3. CMTS1 • One of two test caves at CMTF • In operation since July 2016 • 500 W 2K refrigerator • Test cave + infrastructure • Solid State amplifiers/waveguide distribution • LLRF including piezo control • Interlocks • Magnet power supply • Motor control – Tuners & Couplers • Faraday cup at each end • Rad detectors • Demagnetization coils and power supply • Adaptable for 3.9 GHz operation (late cy 2019) Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

4. Test plan • Developed jointly with Jlab and SLAC partners plus other experts • Plan details adapted for unique capabilities of each test stand • Testing Workshop • Identical results, identical equivalent technique Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

5. CMTS1 Test Sequence • RF calibration (1/2 day) • Initial power rise to 16 MV/m (1/2 day) • Power rise/processing to 21 MV/m (1-2 days) • 60-minute run at peak gradient (Usable Gradient) • FE & Dark current evaluation • Check DecaRad response • Quench detection/protection development • BPM check (parasitic) • LLRF • GDR operation • Magnet check – once leads are cold enough • HOMs spectra (2-3 days parasitically) • 50 K warm up, fast cooldown (≥32 g/s), pump down to 2K, soak (1 day) • RF compensation heaters on • Unit test (1 day) • Cavities at 16 MV/m • Magnet coils at nominal current • Field Emission/Dark current • GDR • ~12 hour run, until coupler temperatures reach equilibrium • Install (11 days) • Align • Cabling • Waveguide • Roof on • Warm frequency spectra • Leak Check • Pre-test Checks (in parallel) • ORC sign-off • Jumpers removed, HOM attenuators proper • Config Control locks • LOTO locks removed • Digitizers running • Tuners powered • Demagnetization (just before cooldown) • 50 K/4 K cooldown (3 days) • Stabilize/soak (10 hours) • Enable alarms • Pumpdown to 2 K (1/2 day) • Stabilize/soak • RF compensation heaters off • During soak (or prior) (~ 1day) • Roof blocks & gate locked • Cave secure • Cavities on resonance/HOMs • Microphonics assessment • Qext set to 4.1E7 Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

6. CMTS1 Test Sequence (2) • Single cavity Q0 (1-2 days) • RF Compensation off • Determine optimum JT valve position • Heater run • No power run • Set constants for real-time Q0 • Cavities at 16 MV/m one at a time • No power run in-between • Pre warm-up review • Test complete/Warm-up (3-4 days) • Detune cavities back to warm frequency (+40,000 steps) • Static Heat Load • Duration • Install: 18 (14) days • Test: 13 (7) days • Warmup & remove: 8 (7) days • Idle: 18 (0) days 50 days at CMTS1 Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

7. LCLS-II 1.3 GHz Acceptance criteria - Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

8. LCLS-II performance summary *No VTS administrative limit **21 MV/m is CMTF administrative limit ***50mR/h wall radiation detector and/or 0.5 MV/m below quench limit Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

9. F1.3-14 characteristics – an example • Small amounts of field emission and dark current detected during cw operation • Cavity #7 onset at 14 MV/m, but low levels to peak gradient • Dark Current from #8 detected at end cap Faraday cup • 1-hour Usable Gradient runs on each cavity • Single cavity Q0 measurements • 32 g/s fast cooldown • average Q0 is 3.1E+10 • 4 cavities tested twice due to unstable position of JT valve on first attempt • Two unit tests • Thermalization ongoing during first one (10 hours) – 3 days after reaching 2 K • Much stabler conditions for second (10 hours) Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

10. Field Emission/Dark Current (F1.3-14) 14 MV/m Cavity #7 Field Emission 10-20 MV/m 16 MV/m Cavity #8 Dark Current End cap:0.1 nA • Cavity #7 exhibits low level field emission with onset at 14 MV/m • Small amounts of detectable dark current from cavity #8 • 0.1 nA peak, end cap only • during unit test only • not a sustained signal • visible only at higher gradients (≥16 MV/m) Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

11. Unit test Coupler Innner Conductor Temperatures Coupler 50 K Temperatures 60 C 120 K 18 hours 18 hours 50 C 60 K • All cavities powered at once • many hour duration • >128 MV sum achieved & maintained • GDR operation – all cavities for as long as possible • Magnet coils at 20 A • Coupler heating <150 K • Phase cavities with any detected dark current (rare) Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

12. Microphonics Acceptance limit is 10 Hz peak Early issues with thermoacoustic oscillation induced microphonics In recent times overall excellent performance Thermalization has an effect – a few days to reach equilibrium and minimize Data capture typically for at least 30 minutes F1.3-14 After cooldown 7 Jan 2019 F1.3-14 Unit test 17 Jan 2019 courtesy Contreras-Martinez Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

13. Supplemental tests - microphonics this week ‘the good old days’ • Original results well documented • Various lines of inquiry purused • Internal working group convened • Ideas solicited from partners • Systematic pursuit of possible sources • Success – finally! • Continue to assess on every cryomodule LCLS-II QA/QC Audit | Nov 2018

14. Q0 measurements Mass flow technique • Dp/Dt technique attempted 32 g/s nominal fast cooldown 3-fold independent analyses Low Q0 correlated to known cavity material with poor flux expulsion Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

15. Performance - Q0 Excel (Harms), real-time calculated, Matlab (Posen) • Fermilab technique – mass flow • Entire cryomodule, one cavity at a time, tested in ~ 1 shift • Large data set (45 minutes) • Mature technique, can be carried out by Operations crews as schedule allows • Multiple analyses yields excellent agreement (within 7%) LCLS-II QA/QC Audit | Nov 2018

16. LLRF performance • Phase and amplitude stability not explicitly quantized during every test • Design specification/physics requirements: • Phase - 0.01∘ • Amplitude - 0.01% • GDR operation demonstrated during unit tests • All cavities at nominal (16 MV/m) gradient • First in SEL, then switch to GDR one at a time • Microphonics environment is the biggest impact • Slow feedback (piezo) incorporated • Recently GDR demonstrated on all cavities for many hours continuously Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

17. LLRF performance – recent Unit test SSA output all cavities GDR Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

18. Summary • Nearly 3 years of CMTS1 operation • 28-day test cycle is achievable • 15 tests to date • Overall well-performing cryomodules • Lots of work early on overcame microphonics limitation • Mature process, but always evolving Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

19. Thank you for your attention Harms - TTC meeting at TRIUMF | WG1 Session 3 | 5 Feb 2019

20. Performance – FE/Rad detector layout FOX (x-ray) detectors DecaRad locations (mounted on each coupler) Faraday cup (at each end) a Total Loss Monitor (TLM) and SLAC fiber optic cable detector run below and the length of the cryomodule stand Recently, dosimetry is mounted on each cryomodule at each cavity location (x3 – east, west, bottom) to record integrated dose LCLS-II QA/QC Audit | Nov 2018

21. Cumulative Performance – Field Emission LCLS-II QA/QC Audit | Nov 2018

22. Supplemental tests - Q0 • Compare two Q0 protocols • Dp/Dt- Jlab • Mass flow – Fermilab • Dp/Dt method attempted at Fermilab • Results compared to mass flow • Data provided to Jefferson lab for analysis • Alternate ‘hybrid’ method tried LCLS-II QA/QC Audit | Nov 2018

23. Operational Readiness Clearance • Prior to every test 2 ORC’s are required • Cooldown • Cold powered operation • Some delays have resulted • Cryo ORC • requires all necessary Engineering Notes are reviewed and approved • Final approval by Cryo dept. head • Cold powering ORC • Initially carried out by ESH&Q representatives • Delegated to test lead since F1.3-03 • Hardcopy sign-off prior to cryomodule being powered • Ensure each system leader physically comes to CMTF LCLS-II QA/QC Audit | Nov 2018